1. Field of Invention
The invention relates to an image forming apparatus such as a color laser printer.
2. Description of Related Art
As an electrophotographic color laser printer, there exists a so-called tandem color laser printer that includes a plurality of processing units, each of which has a developing agent hopper, a developing roller and a photosensitive drum, with respect to toner colors of yellow, magenta, cyan, and black.
In the above tandem color laser printer, toner images of the respective colors are formed on the respective photosensitive drums at almost the same instant by which toner particles stored in the developing agent hopper are supplied onto the photosensitive drum by the developing roller in each of the processing units. Therefore, a color image can be formed at a speed that is almost the same as an image forming speed of a monochrome laser printer.
As the above tandem color laser printer, Japanese Laid-Open Patent Publication No. 9-274423 discloses a color laser printer that is structured as described below. In each processing unit of the color laser printer, a photosensitive drum is disposed opposite to a conveyor belt for conveying a sheet. A developing roller is disposed on one side of the photosensitive drum. A recording head, which exposes the photosensitive drum to light in order to form an electrostatic latent image thereon, is provided opposite to the conveyor belt while sandwiching the photosensitive drum therebetween.